# D
from collections import Counter
n = int(input())
c = list(input())
d = Counter(c)
# print(d)
# print(d["R"])
e=Counter(c[:d["R"]])
# print(e["R"])
print(d["R"]-e["R"]) from collections import Counter n = int(input()) n int(input()) int input() input c = list(input()) c list(input()) list input() input d = Counter(c) d Counter(c) Counter c e=Counter(c[:d["R"]]) e Counter(c[:d["R"]]) Counter c[:d["R"]] c :d["R"] d["R"] d "R" print(d["R"]-e["R"]) print d["R"]-e["R"] d["R"] d "R" e["R"] e "R" e=Counter(c[:d["R"]]) Counter(c[:d["R"]]) e d = Counter(c) Counter(c) d n = int(input()) int(input()) n c = list(input()) list(input()) c
# D
from collections import Counter
n = int(input())
c = list(input())
d = Counter(c)
# print(d)
# print(d["R"])
e=Counter(c[:d["R"]])
# print(e["R"])
print(d["R"]-e["R"])